The present invention is generally related to the field of communications and, more particularly, to a CMOS transconductor with increased dynamic range.
Complementary metal-oxide semiconductor (xe2x80x9cCMOSxe2x80x9d) transconductors have a wide range of applications in the field of communications, among other fields. CMOS transconductors, also known as voltage-to-current (xe2x80x9cV-Ixe2x80x9d) converters, are employed, for example, in various circuits of communications systems, such as intermediate frequency (xe2x80x9cIFxe2x80x9d) transmitters and receivers. Another example of an application of CMOS transconductors is in IF filter circuits, also utilized in communications systems, such as frequency selective networks made up of CMOS transconductors and capacitors.
A typical configuration of a CMOS transconductor circuit 100, as is known in the art, is shown in FIG. 1. As shown, the CMOS transconductor circuit 100 includes several components. The transconductor circuit 100 includes several CMOS field-effect transistors (xe2x80x9cMOSFETsxe2x80x9d). The MOSFETs 102-106 are electrically interconnected in a configuration that provides voltage to current conversion between the inputs 108, 109 and outputs 110, 111 of the transconductor circuit 100.
The transconductor circuit 100 includes two voltage input terminals 108, 109 that connect to the gate terminals of the MOSFETs 104 and 105 respectively, as shown. These MOSFETs 104, 105 accordingly make up the input stage 101 of the transconductor circuit 100. Also as shown, the transconductor circuit 100 includes two current output terminals 110, 111 that connect at the nodes between the drain terminals of MOSFETs 102 and 104 and between the drain terminals of MOSFETs 103 and 105, respectively, of the transconductor circuit 100.
Finally, the transconductor circuit 100 includes a voltage supply rail 112 which provides a voltage to the transconductor circuit 100 via the source terminals of MOSFETs 102, 103. Also, the transconductor circuit 100 includes a ground 118 electrically connected to the source terminal of MOSFET 106 which may consist of, for example, a terminal connected to a common ground point in the transconductor circuit 100. Further, the transconductor circuit 100 includes MOSFET bias inputs 114, 115 that provide a bias signal to MOSFETs 102, 103, 106 via their respective gate terminals.
A CMOS transconductor or V-I converter, such as the transconductor circuit 100 described above, has several basic operating characteristics, as is known in the art, which are described in the following. The input linear range (xe2x80x9cVin,maxxe2x80x9d) of a CMOS transconductor is the maximum input voltage at which the transconductor can still perform substantially linear voltage-to-current conversion. The transconductance value (xe2x80x9cgmxe2x80x9d) of a CMOS transconductor is a value that is approximately equivalent to the ratio of the output current (xe2x80x9cIoutxe2x80x9d) to the input voltage (xe2x80x9cVinxe2x80x9d) of the transconductor. The total integrated output noise current (xe2x80x9cIn,rmsxe2x80x9d) is the noise current produced by a CMOS transconductor integrated over a given bandwidth. This characteristic determines the minimum resolvable output signal of the transconductor and is also referred to as the minimum detectable output current. The power consumption (or power dissipation) of a CMOS transconductor is proportional to the bias current (xe2x80x9cIbiasxe2x80x9d) for a class-A transconductor.
A CMOS transconductor also has the basic operating characteristic values of input impedance, output impedance, 3 dB bandwidth, and minimum-required voltage headroom (xe2x80x9cvoltage headroomxe2x80x9d) (i.e., the capability of the transconductor to operate from low supply voltages), which are understood in the art. Further, the maximum output current (xe2x80x9cIout,maxxe2x80x9d) of a CMOS transconductor can be defined as the product of the transconductance value times the input linear range. Finally, a CMOS transconductor has the basic operating characteristic value of the dynamic range (xe2x80x9cDRV-Ixe2x80x9d), which is defined as the ratio between the maximum signal and the minimum signal that the transconductor can reliably process. The dynamic range can be determined by the ratio of the maximum output current to the minimum detectable output current, that is:                                           DR                          V              -              I                                =                      20            xc3x97                          log              10                        xc3x97                          (                                                gm                  xc3x97                                      V                                          in                      ,                      max                                                                                                            2                                    xc3x97                                      i                                          n                      ,                      rms                                                                                  )                                      ,                  ⅆ          B                                    Eq        .                  xe2x80x83                ⁢        1            
An important goal in the design of circuits utilizing CMOS transconductors is to obtain a high dynamic range. Typically this can be achieved by paralleling one or more CMOS tranconductors that are utilized in a circuit. However, this xe2x80x9cbrute forcexe2x80x9d approach to increasing the dynamic range of the circuit has the significant consequence of increasing the power consumption and chip area of the circuit. For example, for every 3 dB increase in dynamic range achieved by adding a transconductor in parallel to a circuit, there is a 6 dB increase in power consumption of the circuit and a corresponding increase in chip area to facilitate the added transconductor.
Thus, a need exists for a CMOS transconductor with increased dynamic range that does not suffer from the increased power consumption and chip area requirements of prior art transconductor circuits.
The present invention provides a CMOS transconductor that operates with increased dynamic range while maintaining one or more other basic operating characteristics at substantially the same value in comparison to a prior art transconductor circuit.
Briefly described, in architecture, one embodiment of the present invention, among others, can be implemented as an input stage circuit comprising several pluralities of transistors with each plurality of transistors configured such that certain terminals of the transistors are electrically connected, and the several pluralities of transistors are also electrically interconnected through one or more terminals of each plurality of transistors.
The present invention can also be viewed as providing methods for providing a CMOS transconductor that operates with increased dynamic range while maintaining substantially the same other basic operating characteristics in comparison to a prior art transconductor circuit. In this regard, one embodiment of a method of the present invention, among others, can be broadly summarized by the step of modifying an input stage of an existing transconductor circuit to provide a transconductor circuit that operates with increased dynamic range while maintaining one or more other basic operating characteristics at substantially the same value in comparison to the existing transconductor circuit.
Other features and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.